Chemical nickel plating processes and baths therefor



creases.

. CHEMICAL NICKEL PLATING PROCESSES AND BATHS THEREFOR Gregoire Gutzeit, Highland, Ind., Paul Talmey, Barrington, 111., and Warren G. Lee, East Chicago, Ind., assignors to General American Transportation Corporation, Chicago, 1111., a corporation of New York N Drawing. Application December 29, 1954 Serial No. 478,492

29 Claims. (Cl. 117-130 The present invention relates to improved, processes of chemical nickel plating of catalytic materials employing baths of the nickel cation-hypophosphite anion type and to improved baths therefor, and more particularly to such processes and baths involving a continuous system of the character of that disclosed in U.S. Patent No. 2,658,839, granted on November 10, 1953, to Paul Talmey and William J. Crehan. This application is a continuation-in-part of the copending application of Gregoire Gutzeit, Paul Talmey and Warren G. Lee, Serial No. 376,968, filed August 27, 1953, now abandoned. I

The chemical nickel plating of a catalytic material employing an aqueous bath of the nickel cation-hypophosphite anion type is based upon the catalytic reduction of nickel cations to metallic nickel and the corresponding oxidation of hypophosphite anions to phosphite anions with the evolution of hydrogen gas at the catalytic surface. The reactions take place when the body of catalytic material is immersed in the plating bath, and the eX- terior surface of the body of catalytic material is coated with nickel. The following elements are catalytic for the oxidation of hypophosphite anions and thus may be directly nickel plated: iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum. The following elements are examples of materials which may be nickel plated by virtue of the initial displacement deposition of nickel thereon either directly or through a galvanic effect: copper, silver, gold, beryllium, germanium, aluminum, carbon, vanadium, molybdenum, tungsten, chromium, selenium, titanium and uranium. The following elements are examples of non-catalytic materials which ordinarily may not be nickel plated: bismuth, cadmium, tin, lead and zinc. The activityof the catalytic materials varies considerably and the following elements are particularly good catalysts in the chemical nickel plating bath: iron, cobalt, nickel and palladium. The chemical nickel plating process is autocatalyticsince both the original surface of the body being plated and the nickel metal that is deposited on the surface thereof are catalytic; and the reduction of the nickel cations to metallic nickel in the plating bath proceeds until all of the" nickel cations have been reduced to metallic nickel, in the presence of an excess of hypophosphite anions, or until all of the hypophosphite anions have been oxidized to phosphite ions, in the presence of an excess of nickel cations.

2,935,425 Patented May 3, 1960 and is particularly objectionable in that it causes the nickel deposit to be coarse, rough and frequently porous. Any 'iine solid particles suspended in the plating bath, or adhering to the walls of the plating vessel, at the plating temperature, initiate the formation of the black precipitate by acting as nuclei.

In a continuous plating process the reactions are maintained substantially at their initial rates by the regeneration of the plating bath, i.e., by the adding thereto of soluble nickel-containing and hypophosphite-containing reagents, as well as an alkali for pH control; however, the problem of preventing the formation of black precipitate in the plating bath and the consequent decomposition thereof is the same as that previously mentioned. Moreover, another practical difliculty is encountered in the continuous plating process that is not encountered in the batch plating process in that there is a considerable build-up of the by-product phosphite therein as time proceeds and as a consequence of the cycling of the bath.

More particularly, while nickel hypophosphite is readily soluble in an aqueous solution, nickel phosphite is much on a commercial scale, the continuous system disclosed in the Talmey and Crehan patent mentioned may be employed; which system involves periodic or continuous regeneration of the plating bath by the addition thereto of appropriate ingredients for the purpose of maintaining substantially constant the composition of the bath as previously noted. More specifically in this system, there are provided a plating chamber and a reservoir; preferably one portion of the plating solution is stored at a relatively low temperature well below the boiling point thereof in the reservoir; and preferably another portion of the plating solution is held as a bath at a relatively high temperature slightly below the boiling point thereof in the plating chamber. The solution is continuously circulated at a low rate from the reservoir to the plating chamber and then back to the reservoir, the solution being heated substantially to the relatially to the relatively low temperature after withdrawal In a batch plating process, the reactions are sloweddown rather rapidly as time proceeds because the anions, as contrasted with the cations, of the nickel salt that is dissolved in the plating bath combine with the hydrogen cations'to form an acid, which, in turn, lowers the pH of the bath, and the reducing power of the hypophosphite anions is decreased as the pH value of the bath de- Moreover, there is a tendency for the early formation in the plating bath of ablack precipitate that comprises a random chemical reduction of the nickel cations. Of course, this formation of the black precipitate comprises a decomposition of the plating bath,

thereof from the plating chamber and before return thereof to the reservoir. The body that is to be nickel plated "is immersed in the bath in the plating chamber and is subsequently withdrawn from the bath in the plating chamber after a time interval corresponding to the thickness of the nickel plating thereon that is desired; and

during such time interval soluble reagents are added to the solution in the reservoir to maintain in the bath in the plating chamber during such time interval substan tially the predetermined composition of the bath previously mentioned, so as to compensate for the ingreclients of the bath that are exhausted during the time interval in the plating chamber. This regeneration of the solution in the reservoirconsists essentially of adding thereto appropriate arnounts of soluble nickel-containing and hypophosphite-containing reagents, as well ;as an alkali for pH control, as previously noted.

'A typical chemical nickel plating bath that may be employed in the continuous process of the'Talrney and Crehan patent is disclosed in US. Patent No. 2,658,841,

3 granted on November 10, 1953, to Gregoire Gutzeit and Abraham Krieg; which plating bath essentially comprises an aqueous acid solution of a nickel salt and a hypophosphite and a buffer in the form of an alkaline acetate; the pH of the bath being within the approximate range 4.5 to 5.6, the absolute concentration of hypophosphite ionsin the bath being in the range 0.15 to 0.35 mole/liter, the ratio between nickel ions and hypophosphite ions in the bath being in the range 0.25 to 0.60, and the absolute concentration of acetate ions in the bath being approximately 0.120 mole/ liter.

In the carrying out of the chemical nickel plating process on a commercial scale employing the continuous system of Talmey and Crehan, it has been discovered that the chemical nickel plating bath of Gutzeit and Krieg is not altogether satisfactory in that the bath does not have as fast a plating rate as is desirable; and moreover, the activity of the bath is within a relatively narrow pH range. Furthermore, nickel phosphite begins to precipitate at a phosphite ion concentration of about 0.07 mole/liter so that the stability of the bath is not that desired, and the useful life thereof is entirely too Ishort.

' The present invention is predicated upon the discovery that plating baths of the nickel cation-hypophosphite anion type mentioned may have their stable life increased, the plating rates thereof may be substantially increased, the useful life thereof may be greatly extended, and the activity thereof with regard to the usable pH .range may be greatly broadened by the addition thereto of both a nickel chelating agent and an exalting additive. More particularly, the plating baths of the present invention have an increased stable life in that the ability thereof to hold nickel phosphite in solution at high phosphite concentrations is enhanced as evidenced by the clarity of the bath (the lack of turbidity thereof). Also, these plating baths have a nickel plating rate of at least 1 mil/hour (0.001"/hour) or expressed in c.g.s. units, of at least 3.5)(10 gm./cm. /min. Moreover, these plating baths have an activity within a broad pH range (4.0 to 11.0); and no precipitation of nickel phosphite takes place therein even at a phosphite ion concentration in some cases as high as 1.0 mole/liter. Further, the plating appearance on both metals and non-metals is excellent (bright, smooth and non-porous); and the adhesion of the nickel plating on both metallic and nonmetallic bodies is excellent (no flaking of the nickel coating in bending, abrading and shock tests).

Specifically, the plating baths of the present invention consist essentially of an aqueous solution of a nickel salt and a hypophosphite and a nickel chelating agent and a separate and different exalting additive. The nickel chelating agent is selected from the group having the general formula:

where: R is an aliphatic radical, X is a functional group containing a dissociable hydrogen atom and selected from the class consisting of:

and Y is a functional group containing a negative atom actmg as a center of coordination and selected from th class consisting of:

'- NH =NH and EN and wherein the functional groups X and Y are in alpha or beta positions to each other.

This group consists of saturated aliphatic hydroxycarboxylic acids and salts thereof, aminoalcohols, polyalcohols, aliphatic keto acids and salts thereof, aliphatic '4 aliphatic aminocarboxylic acids and salts thereof. The

' exalting additive is selected from the group consisting of polyamines, aminocarbonyls, amine-oxydes, heteroalisimple short chain saturated aliphatic monocarboxylic acids including 3 to 5 carbon atoms and salts thereof, simple short chain saturated aliphatic dicarboxylic acids including 3 to 6 carbon atoms and salts thereof, and short chain aliphatic aminocarboxylic acids and salts thereof.

Further, it is pointed out that the short chain aliphatic aminocarboxylic acids and salts thereof are named both as chelating agents and as exalting additives since these compounds possess these two unrelated characteristics as explained more fully hereinafter.

In accordance with the process of the present invention, the chelating agent, if added in suflicient quantity, substantially completely chelated all of the nickel ions in the plating bath, whereby it ties-up the nickel cations almost completely releasing only a small fraction thereof depending on the chelate stability constant (dissociation constant); whereas the exalting additive increases the plating rate of the plating bath. Thus it will be understood that the plating bath, except for the exalting additive, would have an exceedingly low plating rate due to the tying-up of the nickel cations therein. However, this tying-up of the nickel cations in the plating bath is the fundamental factor contributing to the clarity of the solution, preventing the formation of precipitated phosphites therein, and giving the bath an exceedingly long life in spite of the build-up of phosphite ions therein to a concentration'even in excess of one molar. Of course, the chelate of nickel in the plating bath must be water-soluble and of medium stability resulting in a bond strong enough to prevent the nickel ions from forming insoluble nickel compounds, such as the phosphite, the succinate, the

malonate, etc., and mixed basic salts thereof, as explained more fully hereinafter, but having a stability constant low enough to release the nickel cations required for the nickel plating operation permitting the exalting additive to bring about a plating rate of the bath of at least 3.5x l0- gm./cm. /min., as previously explained.

The general composition of a plating bath in accordance with the present invention essentially comprises an aqueous solution of a nickel salt and a hypophosphite (in addition to the nickel chelating agent and the exalting additive), as explained more fully hereinafter; whereby the absolute concentration of hypophosphite anions in the bath is in the range 0.15 to 1.20 moles/liter, and the ratio between nickel cations and hypophosphite anions in the bath is in the range 0.25 to 1.60. The absolute concentration of the chelating agent in the bath is sufiicient to chelate at least 100% of the nickel cations therein, and the absolute concentration of the exalting additive in the bath is at least 0.04 mole/liter. In the plating bath, two separate additives for these two separate functions are employed. The pH of the bath is in the general range 4.0 to 11.0, depending upon the particular ingredients of the bath, as explained more fully hereinafter; and the bath is utilized in the plating chamber of the continuous plating system at a temperature slightly below the boiling point thereof and above C., ordinarily at about 9799 C. The widening of the pH range is particularly desirable because adhesion of the plating to the base metal is improved at a low pH.

In view of the foregoing, it is the primary object of the present invention to provide an improved nickel plating process of the character described, in which the reactions involved are carried out more efliciently and under more stable conditions (clarity of solution) than heretofore, thereby rendering the process more desirable from a commercial standpoint.

Another object of the invention is to provide an improved aqueous chemical nickel plating bath that may be employed with advantage in the practice of the improved process. Y

Another object of the invention is to provide an improved nickel plating process of the character described,

that employs a plating bath of the nickel cation-hypo phosphite anion type containing both a chelating agent and a separate and different exalting additive, wherein the chelating agent substantially completely chelates all of the nickel cations in the bath, and the exalting additive substantially increases the plating rate of the bath obtaining a plating rate thereof of at least 3.5 X- gm./cm. /min.

A further object of the invention is to provide an improved nickel plating process of the continuous type involving an improved plating bath of the nickel cation hypophosphite anion type so that the useful life'thereof is greatly extended in that the plating bath remains clear notwithstanding the presence therein of a phosphite anion concentration as high as one molar.

A still further object of the invention is to provide an improved nickel plating bath of the character described that incorporates a novel combination of chelating agents and exalting additives.

These and other objects and advantages of the invention pertain to the particular arrangement of the steps of the process and of the composition of the plating bath, as will be understood from the foregoing and following description.

In accordance with the process of the present invention, the article to be nickel plated and normally having a catalytic surface is properly prepared by mechanical cleaning, degreasing and light pickling substantially in accordance with standard practices in electroplating processes. For example, in the nickel plating of a steel object, it is customary to clean the rust and mill scale from the object, to 'degrease the object, and then lightly to pickle the object in a suitable acid, such as hydrochloric acid. The object is then immersed in a suitable volume of the bath containing the proper proportions of nickel cations, hypophosphite anions, chelating agent and exalt- .ing additive, the pH of the bath having been, if necessary,

adjusted to an optimum value by the addition of an appropriate acid or base, and the bath having been heated to a temperature just below its boiling point, such as 99 C., at atmospheric pressure. Almost immediately hydro- :gen bubbles are formed on the catalytic surface of the steel object and escape in a steady stream from the bath while the surface of the steel object is slowly coated with metallic nickel (containing some phosphorus). The steel object is ultimately removed from the bath after an ap- 'propriate time interval corresponding to the required thicknessof the nickel coating deposited thereon that is desired. Ultimately the steel object is rinsed ofi with water, and is then ready for use.

With respect to the composition of the bath, it essentially comprises an aqueous solution containing nickel cations, hypophosphite anions, a chelating agent and an exalting additive, as previously noted. For example, the nickel cations may be derived from the nickel chloride, nickel sulfate, etc., and the hypophosphite anions may be derived from sodium, potassium, etc., hypophosphites or various combinations thereof. The chelating agent and the exalting additive are introduced into the bath normally 7 as the acids or as the soluble salts thereof, etc.; and the desired pH of the bath is established by the eventual introduction thereinto of hydrochloric acid or a weak alkali, such as sodium bicarbonate.

The terms cation, anion and ion as employed herein, except where specifically noted, include the total quantity of the corresponding elements that are present inthe plating bath, i.e., both undissociated and dissociated material. In other words 100% dissociation is assumed when the terms noted are used in connection with molar ratios and concentrations in the plating bath. Also hereinafter the expression percent exaltation is employed with the arbitrary definition as the percent increase in the rate of hydrogen evolution with reference to a given-hypophosphite solution resulting the exalting additivei from-the addition thereto of 6 Turning now more particularly to'the introduction'of the nickel chelating agent into the bath, the following examples of saturated aliphatic hydroxy-carboxylic acids have been found to be particularly suitable:

Hydroxyacetic acid (glycollic acid) CHgOH 1 00011 Monohydroxysuccinic acid (malic acid) 0 Hon-o 0 o H OHa--C 0 o n Dihydroxysuccinic acid (tartaric acid) CHOH-O o 0 H HOH -D0OE Gluconic acid 1 CHOE ( Hon).

OOH

Citric acid 0 Hr-C 0 o E E0 --0 o o H His-*0 0 0B Hydroxymalonic acid coon ono'n 000K Trihydroxyglutaric acid coon acid (lactic acid) HOH Beta-hydroxypropionic acid CH|OH H: a I 0011 Alpha-hydroxypropionic The following polyalcohols have been found to particularly suitable:

Trihydroxyalcohol (glycerol) onion Hon Eton 7 Hexahydroxyaleohol (mannitol) a GHIOH HQOH The following aliphatic keto-acids have been found to be particularly suitable:

Pyruvic acid ll CH:CO OH Levulinic acid CHr-PJ-CHz-Cflr-C O OH Of course the saltsof these aliphatic keto acids, particularly the alkali salts thereof, may be employed.

The following aliphatic polyamines have been found to be suitable:

Trimethylamine s)s Propylenediamme cm-crr-o H:

NH: NH

The following aminocarbonyl and amine-oxyde have been found to be suitable:

Semi-carbazide NHr-NH--NH:

Diethylene-imideoxyde (morpholine) /CH:C]E\[: o NH CH f-Ofia The folowing heteroaliphatic dicarboxylic acid has been found to be particularly suitable: Diglycollic acid (3 Hr-C o 0 H l c Hr-G 0 011 Of course, the salts of this heteroaliphatic dicarboxylic acid, particularly the alkali salts thereof, may be employed. a

The following aliphatic amino-acids have been found to be particularly suitable;

Aminoacetic acid (glycine) c HsC 0 0H 7 Hr 'Alpha-aminopropionic acid (alpha-alanine) cHr-t m-coon Ieta;aminopropionic acid (beta-alanine) Hiram-coon Alpha-aminobutyric acid 51 oHr-oHr-oHQ :o0H NH:

Aminosuccinic acid (aspartic acid) OHS-000E A rr-c oon L-" 21 CHr-COOH Iminodiacetic acid Ethylenediaminotetraacetic acid CHs-COOH H2C.-N

CHr-COOH CHz-CO OH CHr-CO 011 Of course, the salts of the amino-acids, particularly the alkali salts thereof, may be employed.

Turning now more particularly to the introduction of the exalting additive into the bath, the previously-mentioned short chain aliphatic aminocarboxylic acids and salts thereof are also particularly suitable as exalting additives.

Furthermore, the following simple short chain saturated aliphatic dicarboxylic acids including 3 to 6 carbon atoms have been found to be particularly useful as exalting additives:

Malonic acid COOBZ 30011 Succinic acid COOH COOH

Glutaric acid (700E Hi? H1O GOOH Adipic acid OOOH H20 Hal Of course, the salts of the simple short chain saturated aliphatic dicarboxylic acids, particularly the alkali salts thereof, may be employed.

The following simple short chain saturated aliphatic monocarboxylic acids including 3 to 5 carbon atoms have been found to be particularly useful as exalting additives:

Propionic acid CH3-CHZCOOH -Butyric acid CH8CH,CH3Q00H Valerie acid Of course, the salts of these simple short chain saturated aliphatic monocarboxylic acids, particularly the alkali salts thereof, may be employed.

As previously noted, the chelating agent mentioned above form water-soluble chelates with the nickel ions in the plating bath, which chelates in the cases of the hydroxycarboxylic acids and the aminocarboxylic acids may be either alpha or beta position respectively forming five-membered or six-membered chelate rings as follows:

As previously noted, the stability of the water-soluble nickel chelates formed in the bath by the chelating additives are variable and the order of stability of some of the nickel chelates produced by some of the hydroxyacids is approximately as follows (from the more stable to the. less stable): tartaric acid, malic acid, gluconic acid, citric acid, glycollic acid. An important factor that enters into nickel chelate formation by hydroxy-acids is the pH of the solution; for instance, the following pH values represent the range in which the chelate of nickel With three hydroxy-acids is stable (i.e., where no nickel phosphite or basic salts are precipitated in the presence of 0.30 mole/liter of nickel phosphite over a range from room temperature to 100 0.):

Citric acid pH 4.6 to 4.8 and 6 .5 to 11.0. Malic acid pH 4.5 to 5.7. Tartaric acid pH 4.5 to 5.0.

For the purpose of studying the increase of the hydrogen gas evolution due to exaltation with the use of diiferent additives including those involved in the discovery of the present invention, i.e., simple short chain saturated aliphatic dicarboxylic acids and aliphatic aminocarboxylic additives, and other additives whichhave been used or suggested for chemical nickel plating baths, tests were made with test solutions of 50 cc. and containing sodium hypophosphite at a concentration of 0.225 mole/liter (to which a trace of nickel salt, i.e. 0.0024 mole/liter, was added to initiate the reaction at a vigorous rate). Pickled pieces of mild steel, 20 cm. area, were introduced for periods of 30 minutes each. Thedifierent test solutions respectively contain no additive, and additives.

additive.

The exaltation test results were as follows:

H2 evolved in 30 min.

from 50 cc. solution Percent Additive (Anion) 0.125 moles/l. at 0.225 moles/1. Exaltation sodium hypophosphite at 98 C.

v, V V 125 Aspartic 250 213 From these exaltation tests, it will be observed that the following anions give exaltation values over 100% (which appears to be the lower limit of practical efliciency): propionic, butyric, valeric, malonic, succinic, glutaric, aminoacetic, aspartic.

As a practical matter, it has been discovered that the soluble propionates, succinates and aminoacetates are the most suitable as they are cheap, readily obtainable upon the market in commercial quantities and produce the desired exaltation to a satisfactory degree.

In the formulation of plating baths in accordance with the present invention, at least 100% of the nickel cations should be chelated so that the ratio of the hydroxyacid/Ni++ is at least two for monobasic and dibasic hydroxy-acids, and at least one for tribasic hydroxy-acids.

In the use of short chain aliphatic aminocarboxylic acids, simple short chain saturated aliphatic dicarboxylic acids and simple short chain saturated aliphatic monocarboxylic acids, it is believed that this phenomenon results from the formation of heteropoly-acids between the organic additive and the hypophosphite' anions which compete with the nickel chelate formation. Thus if the nickel chelate is too stable, insuficient nickel cations are available for deposition and the plating rate becomes low despite the exalting elrect produced by the organic The composite chelating eifect and exalting efiect of the various chelating agents and exalting additives in the plating baths were established by a series of plating tests that were made employing a series of test! plating baths of the general character of those previously dfescribed and as set forth more particularly hereina ter.

In the various plating tests appearing hereinafter weights of nickel plating deposited are reported in gms., and plating rates are usually reported in gm./cm. /min. although occasionally plating rates are reported in mils/hour (i.e. 0.001"/hour).

In a plating bath of the character noted, substantially complete chelating of the nickel ions maintains a clear plating solution but results in a low and impractical plating rate; whereas the addition of an exaltant to the chelating bath will raise the plating rate thereof to a practical value as indicated by the following tests involving Baths A, B, C, D, E, F and G, having the specific compositions indicated hereinafter.

A simple aqueous malic acid plating bath was first prepared that had thefollowing composition:

The pH value was adjusted with NaOH and HCl.

Utilizing this, plating bath, properly cleaned steel samples of"20"cm. area were plated for 10' minutes, the

1 1' volume of the bath being 50 cc. and the temperature thereof being about 98 C., with the following results:

Initial nFl' 4. 50 5. 02 Final in 4. 1e 4. 35 Wt. gain- 0. 057 0. 706 Plating rate, R 10- 2. 85 3. 53

Initial nH 4.50 5. 10 Final in 4. 4. 48 Wt. gain- 0 0701 0.0853 Plating rate, RXlO 3. 51 4. 28

. From a comparison of the plating tests using the Baths A and B, it will be observed that the plating rates are substantially exalted by the addition of the small amount of sodium succinate mentioned, the plating rate of Bath B at the higher pH being very satisfactory.

Then a simple aqueous Z-aminoethanol plating bath was first prepared that had the following composition:

Bath C:

Nickel chloride m.p.l 0.0675 Sodium hypophosphite m.p.l 0.225 Z-aminoethanol m.p.l 0.135 Stabilizing ion: Pb++ p.p.m l

The pH value was adjusted with HCl.

Utilizing this plating bath, properly cleaned steel samples of 20 cm. area were plated for minutes, the volume of the bath being 50 cc. and the temperature thereof being about 98 C., with the following results:

Initial pH 4.50 Final pH 2.54 Weight gain 0.01 Plating rate R 10 0.50

To the Bath C, there was added 0.09 m.p.l. of sodium succinate as exaltant in order to produce the Bath D, and the plating tests were repeated under otherwise identical conditions, with the following results:

Initial pH 4.45 Final pH 4.08 Weight gain 0.0760 Plating rate R l0 3.80

Bath E:

Nickel chloride m.p.l 0.126 Sodium hypophosphite m.p.l 0.094 Hydroxyacetic acid m.p.l 0.092 pH 4.6

Utilizing this plating bath, a properly cleaned steel sample of 20 cm. area was plated for 10 minutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., and the plating rate was 1.84 10" gm./cm. /min.

To the Bath B, there was added 0.06 m.p.l. of sodium succinate as exaltant in order to produce the Bath F, and the plating testwas repeated under otherwise identical conditions and there was obtained a plating rate of 3.43 X 10- gm./ cm. min.

From a comparison of the plating tests using the Baths E and F, it will be observed that the plating rate is substantially exalted by the addition of the small amount of sodium succinate mentioned.

For the purpose of demonstrating that this improvement in the plating rate of the Bath F over the Bath E is not due merely to the increased concentration of an organic additive, an additional aqueous bath was employed having the following composition:

Bath G:

Nickel chloride m.p.l 0.126 Sodium hypophosphite m.p.l 0.094 Hydroxyacetic acid m.p.l 0.152 Stabilizing ion: Pb p.p.m 1.0

It is noted that the Bath G contains no exaltant but an additional quantity of 0.06 m.p.l. of hydroxyacetic acid over that of the Bath F, so that the Baths F and G contain the same concentration of organic additive.

Utilizing this plating bath, a properly cleaned steel sample of 20 cm. area was plated for 10 minutes, the volume of the bath being 5 0 cc. and the temperature thereof being about 99 C., and the plating rate was: 1.80X10- gm./cm. /min.

From a comparison of the plating tests using the Baths F and G, it will be observed that the higher plating rate of the Bath F is due to the exalting additive and not to the total concentration of organic ion present.

A series of plating tests were then conducted demonstrating that the various complexing agents, properly selected as to the obtained stability coelficient, in amounts sufiicient to give substantially complete chelation, and used with the addition of an exal'ting additive, result in chemical plating baths having high rates of deposition.

In a series of these plating tests a number of aqueous baths having the particular compositions indicated below were employed in the plating of properly cleaned steel samples of 20 cm. area, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the following results:

Rate Bath Compositions Initial (gmJcmJ/ pH min.X10 10 minutes No. 1 5. 10 4. 60 Malie acid... m.p.l. 0.16 Sodium succinate m.p.l. 0. 06

odlum hypophosphite.-- m.p.l. 0. 225 Nickel sulfate m.p.l. 0. 09 No. 2 6.90 4. 68 Sodium citrate m.p.l. 0.05 Sodium succinate" m.p.l. 0. 06 Sodium hypophosphite. m.p.l. 0. 225 Nickel sul m.p.l. 0. 0675 No. '-l 7.50 5. 41 Sodium citrate m.p.l. 0. 045 Sodium aminoacetate m.p.l. 0. 09 Diglycollic acid m.p.l. 0. 06 Sodium hypophosphite m.p.l. 0. 225 Nickel chloride m.p.l. 0. 09 No. 4 7. 50 5. 41 0 Sodium citrate m.p.l. 0.045

Sodium aminoacetate m.p.l. 0. 09 Sodium succinate m.p.l. 0. 06 Sodium hypophosphite m.p.l. 0. 225 Nickel sulfate m.p.l. 0.09

Employing the Bath No. 2 (citrate-succinate), it was found that the effect of pH variations is as follows:

pH 10 min. Plating Rate (gm./cm. /min. 10

5 00 3.50-Fair 5 m 3.56-Fair 6 90 4.68G0od 7.65 4.71Good. 7.95 Mil-Good.

l3m ployingthe Bath No.4 (citrate-aminoacetate-sucornate) it was found that the 'efiect of pH variations is as follows:

. In view of the foregoing, it is apparent that the Baths Noel and .4, are most effective in the alkaline range. With certain basic metals, as for instance aluminum, a

pH is desirable.

In another series of these plating tests a number of aqueous baths having the particular compositions indicated below were employed:

Bath compositions: M.p.l.

Hydroxyacetic (glycollic acid) I 0.18 Sodium succinate 0.05 Nickel sulfate 0.09 Sodium hypophosphite}; 0.225 No.

Lactic acid 0.18 Sodium succinate 0.06 N ke fate Sodium, hyp p sphi e. 0225 No 7 V v Malic acid 0.16 Sodium succinate 0.06 Nickel sulfate 0.09 Sodium hypophosphite 0.225

Tartaric acid 0.16 Sodium succinate 0.06 Nickel. sulfate 0.09 Sodium hypophosphite 0.225

Sodium citrate 0.05 Sodium succinate 0106 Nickel sulfate 0.09 Sodium hypophosphite 0.225

Utilizing these plating baths properly cleaned steel samples of 20 cm. area were plated for.1 0 minutes, the volume of the bath being cc. and the temperature thereof being about 99 C., with the following results:

From the foregoing, it will be observed that the Bath No. 6 (lactic acid-succinate) produces the highest plating rate while the Bath No 8 (tartaric acid-succinate) produces the lowest plating rate. This is due to the fact tha the lactic acid nickel chelate is least stable, while the. tartaric acid nickel chelate is most stable. When 0.3 151,111. of phosphite ion is added to these baths precipitation of nickel phosphite takes place in the Bath No. 6 (lactic acid-succinate), whereby the 'Baths Nos. 5-. 7 and 9., are. preferred in t e cont nuous p a n y while the Bath No. 6. may housed a a a y for batch. plating.

" In another. series. of, these plating tests an aqueous iwa's employed:

Bath composition:

Sodium citrate m.p.l. 0.05 Sodium succinate m.p.l. 0.06 Nickel sulfate m.p.l. 0.0675 Sodium hypophosphite m.p.l. 0.225

Ratios:

Ni++/hypo- 0.33 Tribasic hydroxyacid/Ni++ 0.74 Initial pH adjusted with sulfuric acid or caustic soda.

Utilizing this plating bath properly cleaned steel samples of 20 cm. area were platedfor 10 minutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the following results (averages of duplicate tests being reported):

Initial pH 4. 5 4. 5 5. 0 5. 0 5. 5 Final pH..-- 3. 95 3. 95 4. 32 4. 32 4. 30 Weight gain- 0.0531 0.0526 0.0707 0.0691 0.0717 Rate, 2. 66 2. 63 3. 54 3. 46 3. 58 Initial pH..- 5. 5 7. 65 7. 65 7.95 7. 95 Final pH---- 4. 30 5. 0 5.0 5. 22 5. 22 Weight gain- 0. 0706 0. 0940 0. 0941 0. 0925 0. 0873 Rate, 3X10- 3. 53 4. 4. 71 4. 63 4. 37

In view of the foregoing it is apparent that the Bath No. 10 (citrate-succinate) is most effective at 'a pH of around 7.50.

The Bath No. 10 was slightly modified by varying the sodium succinate content to provide three different batches thereof having the following compositions:

Batch Compositions Bath N0. 10 I II III M.p.l. M.p.l. M.p.l. Sodium citrate 0. 05 0. 05 0. 05 Sodium suoeinat .04 0. 06 Nickel sulfate 0. 0675 Sodium hypophosphite 0. 225

Employing these batches of the Bath No. 10 properly cleaned steel samples of 20 em. area were plated in duplicate tests for 10 minutes, the temperature of the bath being about 98 (3., with the following results:

Batches of Bath I I II II III III Sodium succinate-.- 0.02 0.02 0. 04 0. 04 0. 06 0. 06 Initial pH-..' 7. 30 7. 30 7. 30 7. 30 7. 65 7. 05 V 6. 60 6. 60 6. 40 0. 40 5. 0 5. 0 Wt. Gain 0. 0772 0. 0756 0. 0913 0. 0906 0. 094.0 0. 0941 Rate, 3X10 3. 86 3. 78 4. 57 4. 53 4. 70 4. 71

In View of the foregoing, it will be observed that the Batch III of the Bath No. 10 (citrate-succinate) yields the highest'plating rate employing 0.06 mole/liter of sodium succinate.

In another series of these plating tests, an aqueous bath having the particular composition indicated below was employed:

Bath composition:

Initial pHj adjusted with caustic soda and hydrechloricacid.

Utilizing this plating bath properly cleaned steel samples of 20 cm. area were plated for 10 minutes and 60 minutes, the volume of the bath being 50 cc. and the temperature thereof being 99 C. with the following 16 Comparing the Baths Nos. 11,12 and 13, it will be observed that plating rates and 60 minute nickel deposits are greater employing the Bath No. 13 utilizing a Ni++/hyporatio of 0.4 rather than the ratio 0.33 as results: 5 in the Baths Nos. 11 and 12.

In another of these plating tests, an aqueous bath Initial pH 4.5 5,0 5.5 5,0 7.1 having the particular composition indicated below was Plating rate min. test) employed:

R 10 3.51 4.27 472 4.80 4.01 Wt. gainin(60min.) 0.1851 0.1866 0.1880 0.1885 0.1896

10 Bath composition:

The optimum pH for the Bath No. 11 is around neutrality; and in the alkaline range this plating bath Sodium citrate m.p.l..- 0.045 has a tendency to gel. Aminoac tio cid m.p.l 0.18

Another series of plating tests were run for 10 min- Ni k l Chloride ..m.p.l..' 0.09 utes and 60 minutes employing the Bath No. 11, at 5 Sodium hypophosphite ..m.p.l 0.225 variable pH upon properly cleaned steel samples of Ratios: I cm. area, the volume of the bath being 50 cc. and the Ni++/hypo 0.4 temperature thereof being about 99 C., with the fol- Tribasic hydroxy-acid/Ni 0.5 lowing results:

Time of test 10 60 10 60 10 60 10 InltialpH 4.50 4.50 5.10 5.10 5. 00 6.00 7.10 Wt. gain 0.0701 0.1851 0.0853 0.1866 0. 0051 0.1893 0. 0081 Platingrate R 10 3.51 4.28 7 4.81 4.01

In conjunction with these tests, it is noted that at Stabilizing ions: about pH 7.0 the plating rate is almost 5.0X10- Pb++ pm... 1 gm./cm. /min., i.e. over 1.4 mils/hour. Te++ p.p.m. 1

In passing, it is noted that the optimum pH, which is Initial pH adjusted with HCl and NaOH. around 4.6 for a succinate bath (without malic acid) shifts toward the neutral point in a bath containing all Utilizing this plating bath properly cleaned steel samthe nickel cations in the form of a chelate. As will be ples of 60 cm. area were plated. The bath was employed seen hereinafter the contrary is true when an aminoin a continuous plating system having a plating chamber acid is used as the chelating agent in conjunction with volume of 300'cc., the volume of the bath being 2 liters succinate asthe exalting additive. and the temperature thereof being about 99 C.; and

In order to determine the effect of increased sucthe following results were obtained: cinate concentrations two additional substantially identical plating tests were run at pH 5.5, one with the Bath Initial pH 6.60 No. 11 containing sodium succinate at a concentration 40 Final pH 6.35 of 0.06 m.p.l., and another with an otherwise identical Weight gain 1.1245 bath (No. 12) containing sodium succinate at a concen- Rate R 10 5.21 tration of 0.12 m.p.l., with the following results: Duration of test, min. 36

Flow rate solution, cc./min. 55.5 Bath Compositions No. 11 No. 12 i In another of these plating tests, an aqueous bath hav- Sodium succinate (m.p.l.) 0.05 0.12 ing the particular composition indicated below was em- Initial n 7 5 ployed: Plating rate (10 min. test) RXlO 4.73 5.12

A continuous plating test was conducted utilizing the Bath composition g, Bath No. 12 containing sodium succinate at a concen- Bath 5 tration of 0.12 m.p.l., as previously noted; and a plating Sodium citrate m.p.l 0.045 rate of 5.09 10 gm./cm. /min. was achieved. Malic acid m.p.l 0.09

In another series of these plating tests, an aqueous Sodium succinate .m.p.l 0.06 bath having the particular composition indicated below Nickel chloride m.p.l 0.09

, was employed: Rant}? Hh i+ ypo- 0.4 ggfi gi f g Tribasic hydroxy-acid/Ni i 0.5 Malic acid mp1 018 Malic ac1d/Ni++ 1.0 T u Stabilizing ions: Te++ p.p.m 1 103211?511135312?:::::::::::::$:Ii:: 3:83 Initial PH adjusted with HQ and N30 Sodium hypophosphite m.p.l.. 0.225 Ratios: Utilizing this bath, properly cleaned steel samples of Ni++/hypo" V cm. area were plated. The bath was employed 'in a I-Iydroxy-acid/Ni 2- continuous plating system having a plating chamber vol- Utilizing this plating bath, properly cleaned steel samof 9 the volume 9 the bath b61313 2 hters and ples of 20 cm. area were plated for 10 minutes and 60 the telnpz'lature therem tfemg about 99 and 1 minutes, the volume of the bath being 50 cc. and the followmg results were obtained:

e l wtflrgrlpeglalttigre thereof being about 99 C ,l with the fol o Inmal p 6.80 Final pH 6.20 Weight gain 1.8397 i littig fiazirani15501152151: 3:38 2% it? Rate 1 x 4.90 Wt. gainin60 min. 0.2130 0.2210 0 2 27 Durat on of test, mm, 66

Flow rate soln., cc./min. .1 60.6

109.0 1. 195 f- 040515545 0 05. 90. 429115001109 i1 8 the particular composition indicated below was .emp ed:

lowing results were obtained:

Bath composition: 0 5 GWEN 1 2 3 1 p int ng: g 1

. l1 Sodium cmafe V\ t. Ggin 2.84 3. 92 4.04 3.86 Sodium succmate m.p.l 0.06 gata Rxlt l u (M 4.3; 5. 5.1 5.2% Nickel sulfate m.p'.l 0.0575 51%? .e% ,fii,2c. .nm 5 42 45- 44 S i y-lp -p m.p-L x0 Cumulative Depletion, percent 12.7 30.1 50.7. 07.9

Ratios: p 5

' h 133 hi 70 0f d p e n 5 l arbitrary measure l Tribaksic hydmxyjagidflfifi Int-Fl", 0,74 ggltgunt'of mckel taken out, as a depos1t, of the original Stabilizingions: In another ofthese plating tests, an aqueous bath-hav- Pb++ p.p.m 5 jing the particular composition indicated below was zn++ p.p. m 1 p y 5 Initial pH adjusted with NaOH. Bath composition: BathNo.l84-

Utilizing this bath, properly cleaned steel samples of S 1 0,0725 60cm. area were plated. The bath was employed in a o r continuous plating system havinga plating.chamber vol- Sodlum Succlnate -,P- ume of 300 cc., the volume'ofthe bath being 4 liters and Nickel chloride m.p.l.. 0.09 the temperature thereof being about 99 C. In this plat- 5 I i hypophosphite ;1 0225 mg test, the plating bath was regenerated after each Ratios, cycle by the "addition of'nickel sulfate, sodium hypophos- NIH/11 o 4 phite and sodium bicarbonate intheres'ervoir, in the manner disclosed in the Talmey and-Crehan patent; and Tl'lbaslc Y Y' the following results were obtained: 1 I Stabilizing ion: Pb++ p.p.m' 4

FinalpH 0. 0.00 0. 30 0.50 ,0. 40 -0. 0. 000 5111.... 1.=5072;=1.'9073 2.3271 2.09107 1.9408 2.1617 2.0493 Rate R. 10. 4.70 4.74 5.40 5.10 5.00 4.14 4.33 Durationof cycle (In 56 '67 72 88 66 87 102 Flow rate'soln.,cc.lmi 7l.4l M60 :55.=5 45.5. .6016 106' In another of these plating tests, an aqueous hath hay,- Utilizing this bath, properly cleaned steel samples of ing the particular composition indicated below was 80 cm; area were plated. The bath was employed in a employed: continuous plating system having a plating chamber vol- .ume of 300 cc., the volume of the bath being 6 liters and Bath composition: 5 the temperature thereof being about 99 C. In this plat- Bath No. 17- v ing'test the plating bath was regenerated after each cycle s di i m, 1 10,03 by :the'addition of nickel chloride, sodium hypophosphite S .0116 and sodium bicarbonate 1n the reservoir in the manner gi i V g I 09 disclosed in the-flalmey and Crehan patent; and the folae 'p lowing. results were obtained (duplicate tests being Sodium hypophosphite ;m.p.l 072 25 3110385);

Q?.1 T9-.--.--.-.--'---.-'--'- v V 1 2 3 4 .6

0.49 0.49 0.55 0.50 0.00 0.50 0.50 0.52 0.50 0.50 0.28 0.32- 5.05 5.01 5.00 5.80 5.79 6.85 5.90 '0. 02 4 5.29 4.90 4.10 a. 09 3.90 4.89 5.88 4.09 5.70 4,149 Rate,.RX10 5.00 5.25 4.45 4.39 5.08 5.00 5.35 5.55 5.51 5.45 Duration-otCycle,'Min us 110 110 105 98 109 138 110 1-29 103 FlowrateSoln.,cc./mi n 49- 49 40 54 5s 52 41 52 44 .55 ,CumuL-Deph PercenL 10.7 14.7 28.7 20.0 41.3 42.0 50.7 50.5 75.0 00.9

Ratios: In another of these plating tests an aqueous bathhaving the particular composition indicated below was Tribasichydroxy-acidfiNi 0.09 P Stabilizing ion: Pb++ -.m -5 Bath "Bath NO.

Utilizing this bath properly cleaned steelw'samples of Sodium citrate 1 0 45 cm? arealwere plated. h'lhe .bath'lwas enilployedin 1a sodiumraminoagetate (m9 'contmuousp atlng system avmg a p atmg c an er vo ,70 Nickel chloride mp l ()9 time of 300 co, the volume of the bath be1ng-4 hters and S h h hi 1 0 225 the temperature-thereof being about 99 C. In this plat o ypop osp te ing test, the plating bath was regenerated'after each cycle Q i by the addition'of nickel sulfate, sodium :hypophosphite YP 0.4 and sodium bicarbonate in the. reservoir in the manner 1 Tribasic hydroxy-acid/Ni++ 0.5

20 sulfate and sodium bicarbonate and a new sample of 20 cm. area was plated for 60 minutes in the regenerated bath. The results of these companion tests were as follows:

and the temperature thereof being about 99 C. In this plating test, the plating bath was regenerated after each cycle by the addition of nickel chloride, sodium hypooriginal Re mgr. phosphite and sodium bicarbonate in the reservoir, in the bath bath manner disclosed'in the Talmey and Crehan patent; and km 1 H 0 the following results were obtained. 12 2:8

Wt. gain 0. 3215 0. 3464 Cycle N 1 2 39 :38 3:28 In another of these plating tests an aqueous bath hav- Wt. a'in. 1.2182 1. 6638 ing the particular composition indicated below was em- R e, RXIO 3. 91 3.62 1 Duration of cycle (mln.) 52 85 p y Flow rate soln., ceJmln 77 47.1

Bath composition:

In another of these plating tests, an aqueous bath hav- Bath No. 22- ing the particular composition indicated below'was e M li id ,1 0,09 ployed: Aminoacetic acid ..m.p.l 0.09 Bath composition: Nickel chloride 'm.p.l 0.09

Bath Sodium 11 o llOS hite ....m. .1 0.225

Sodium citrate m.p.l-.. 0.045 yp p p a P Ratios. 1 Sodium ammoacetate m.p.l 0.09 0 4 Diglycollic acid m.p.l 0.06 [hypo """T Nickel chloride m.p.l 0.09 Hydroxy-ac1d/N1++ 1.0 Sodium hypophosphite m.p.l..- 0.225 Amino/Ni++ 1.0 Ratigg: h 04 Stabilizing ions:

i++/ YP p ,m 1.0 Tribasic hydroxy-acid/Ni++ 0.5 6+ 1 p p m I 1 0 Stabilizing ion: Pb++ p.p.m 2.5 "r Initial pH adjusted with HCl and NaOH. 111ml P adlusfied. W 3- Utilizing this bath, properly cleaned steel samples of Utilizing this bath, properly cleansd steel samples of 60 cm. area were plated. The bath was employed in a 60 cm. area were plated. The bath was employed in a continuous plating system having a plating chamber continuous plating system having a plating chamber volume of 300 cc., the volume of the bath being 4 liters volume of 300 cc., the volume of the bath being4 liters and the temperature thereof being about 99 C. In this and the temperature thereof being about 99 C. In this plating test, the plating bath was regenerated after each plating test the plating bath was regenerated after each cycle by the addition of nickel chloride, sodium hypocycle by the addition of nickel chloride, sodium hypophosphite and sodium bicarbonate in the reservoir, in the phosphite and sodium bicarbonate in the reservoir in the manner disclosed in the Talmey and Crehan patent; and manner disclosed in the Talmey and Crehan patent, and the following results were obtained: 5 the following results were obtained:

cycles. I 1 2 3 4 5 6 7 8 9 Dur. of cycle (min) .76 64 79 82 81 71 60 Flow rate 50111., cc./min 52.7 72.77 62.6 50.6 66.6 46.8 49.4 56.3 66.6

Hardness tests were performed upon these samples 55 plated with the Bath No. 20 with results between 600 OycleNo 1 2 3 4 0 and 680 Vickers units.

In another of these plating tests, an aqueous bath hav- Initial H. 6.50 6.50 7.00 6.90 0.80 mg the particular composition indicated below was em- 23: 3 92 33 25%; 2- 12 ployed: 60 Rate 11x10 4.54 4.42 4.91 4. 66 4.81 Duration of cycle (mln.) 25 31 39 94 92 B th o iti Flow rate So1n., ce./mln. 80 58.1 61.3 42. 6 43. 7

Bath No. 21--'- Malic acid 0.18 In another of these plating tests an aqueous bath havsodium succinate (L06 ing the particular composition indicated below was em- Nickel sulfate m .p,1 0,09 ployed: Sodium hypophosphite ;..m.p.l 0.225 B mp sition; Ratios: Bath No. 23-

0.4 Malic acid m.p.l 0.18 Hydr y-acid/Ni++ Z0 Sodium succinate m.p.l 0.06 S bili i f L0 N1cl el sulfate ..-m.p.l 0.09 Initial pH adjusted with HCl and NaOH. i y hyPoPhosPhue -P- i at1os: Utilizing this bath, a properly cleaned steel sample of Ni++/hypo- 0.4 20 cm. area was plated for 60 minutes in- 100 cc. of the Hydroxy-acid/Ni++ 2.0 bath at 99 C.; then the bath was regenerated with nickel Stabilizing ion: Pb++ p.p.m 3.0

Utilizing bath, properly preparedgeneral'pmose Bakelite? samplesof 7.0 cm. area were plated. The bath was employed in :acontinuous platingsystem having a plating chamber volume of 3.00. 66;,10116 volume of the ulumeot .300: the-volume. efzthe bath b. .i!. 8;.;1:i1.i.t.l' and the tempena ure theneo "b ing about 100 -C. in

this plating test, the p ting bath was reg ner ted aft each cy le by the ddition of nickel chloride, sod u bath being 4 liters and the temperature thereof being 5 hypopghosphite and sodium bicarbonate in the reservoir about 99 C. In this plating test, the plating bath was inthe mannetdisclosed in the Talmeyand Crehan patent;

regenerated after each cycle by the addition of nickel and the following results were obtained:

Cycle No 1 2 3 4 5 6 7 8 InltlalpH 5. as. 5.39. 5. a7. 5. 33 5.157, 115.38 5.44 Flnal n- .5. s 4. 01 5. 07 4. 90 5.11 5.07 5. 2s Wt.galn-(gms.-)- 4.11 "3.62 "4.82 3.50- 4.03* :00 4.95 Time, min .105- 100. 120; -04 1 3; K .126 121 Soln. flow rate, cc./min 54 .57 45 ,61 W65; 145 47 Platingrate R 10 4. 00 4. 5a 4.77 41s 4190 4.00 5.13 Turnover'ot Nt,m.p.l..-- 0.0235 0.0332 0.0451 0.0550 0.0563 0.0790 0.0029

sulfate, sodium hypophosphiteand sodium bicarbonate in the reservoir, in the manner disclosed in the Talmey In another of these plating itests, an aqucous ibathhaving the particular composition indicated below was'mand Crehan ,patent; and ,thefollowing'results ,fwere'obployed: tained:

Cycle No 1 2 3 4 5 6 7 3.86 4.14 4.07 4.6 4.10 Duration Cycle (mln.)- 150 240 150 240 150 150 140 Flow ratesoln.,-cc./min. 27 22 27 22 27 27 29 Gumul. DepL, percent 19.0 136.0 50.5 67.5 87.9 106.5 135.2

Prior to plating thesarnples of Bakelite were pre- Bath'composition: pared in accordance with the methods disclosed in U.S. -Bath No. 101.111. Patent No. 2,690,401, granted on September 28, 1954, 1 Nickel chloride ..p 0.0675 to Gregoire Gutzeit, William J. Crehan and Abraham Sodium 'hypophosphite 0.225 Krieg, and in U.S. Patent No. 2,690,402, granted on Malic acid 0.06 September 28, 1954, to William J. Crehan. Specifically, Lactic acid 0.2025 the outer layer or skins of the Bakelite samples were Sodium succinate 0.12 removed mechanically with fine emery cloth; and then' 40 Phosphorous acid 0.4

they were soaked in an aqueous solution containing 35 p-.p;m. of palladium chloride for 72 hours; the samples were then thoroughly rinsed in water, dried, and the palladium chloride was reduced to metallic palladium in in hot aqueous solution of sodium hypophosphite (0.335 m.p.1.) until bubbling .sudsided. The nickel coatings on theBak elite' samples were of excellent quality, bright and smooth, and adhesion was excellent, resisting-both thermal shockfro'm -4.0 C. .to 100 (3,, as well as mechanicalshock.

In another of these plating tests an aqueous bath having the particular composition indicated below was .employed:

Bath composition:

.BathlNo..24=-,-

Nickel chloride m.-p.l 0.0675 Sodium hypophosphite ..m.p:l. 0.225

and initially: 0.4 m.p;l. .of phosphite ions were introduced i into the bath for the purpose of examining thekability ,of the bath to hold phosphite at a reasonably high phosphite ion concentration.

The results of this test were as follows: 7

Cycle No 1 2 3 4 -5 a 7 Initial n 4. 74 4. 74 4. 72 4. 75 4.75 4. 7s 4. 77 ,mnal n 1 4. 50 4. 69 4. 52 4. 01 4. 4.50 .4. 0s wn ain. gms..--- 4. 07 3.08 4. 00 3.80 .3. 7.5 4. 07 4.20 Time, min 120 101 05 v as 105, 123 127 .Soln. Flow-rate, cc:/m:ln 47 56 60 '54 .46 .46 Plating rate, RX10 4.85 4-55 5.08 5. 40 4.45 4,14. 4.14 .Additlonoilbfi, p.'p.m.... None None None 1 None 'None None Malic acid m.p'.l 0.13'5 p In passing, it is notedithat the plating rate which was Sodium succinate ..;m'.p.-l 0.06 0 up to4.5 10'- gm./cm. /min. in cycle 'No. 4 dropped :Pb as stabilizing ion 4 ..p.p.m.. "2.-0 to 4.1'4 .10- gm./cm. /min. in cycle No. 5, after the '(Water to make on liter of solution.)-

Utilizing this bath properly cleared steelx'samples of cm. area were 'plated. The bath was .employed in feeding into the bath of only 1 p.p.m. of .Pb++. .Even as little as 0.25 p.p.m. of Pb++ may result 'in a dropof the plating rate from about 5.0 "l'0'- to 4.'5 '10- grnJgmWmiuainBath No. 25'. -Q11 the other hand, :the

acontinuous plating system having a plating chamber 5 Bath, .No. .25 does notrespond disadvantageouslypas to plating rate, to the addition of other stabilizing ions and molecules (Te++ etc., sulfhydric compounds, etc.) as disclosed in thecopending application of Paul Talmey and Gregoire Gutzeit, Serial No. 359,428, filed June 3, 1953.

In another series of these plating tests, an aqueous bath having the particular composition indicated below was employed:

Bath composition:

Bath No. 26-

Nickel (as chloride) m.p.l 0.0675 Sodium hypophosphite m.p.l 0.225 Glycerol m.p.l 0.135 Stabilizing ion: Pb++ p.p.m.... 1 pH adjusted with NaOH or HCl.

It is noted that two molecules of glycerol can complex three molecules of nickel: whereby the polyalcohol in the Bath No. 26 is in excess.

Utilizing this plating bath, properly cleaned steel samples of 20 cm. area were plated for 10 minutes and 60 minutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the following results:

In view of the foregoing, it will be understood that the bath containing glycerol alone, in amounts sufiicient to complex completely the nickel ions, gives 10 minute plating rates below 1.0X10- gm./cm. /min.

A plating bath (No. 27), identical to the Bath No. 26 (except that it also contained 0.06 m.p.l. of sodium succinate) was then prepared; and utilizing this plating bath properly cleaned steel samples of 20 cm? area were plated for 10 minutes and 60 minutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the following results:

Plating time 10 minutes 60 minutes Initial pH 4. 50 5. Wt. gain 0. 1216 0. 1580 Plating rate, RXIOL Turbidity none none none none In another series of these plating tests,- an aqueous bathhaving the particular composition indicated below was employed:

Bath composition:

Bath No. 28 M.p.l. Nickel chloride 0.0675 Sodium hypophosphite 0.225 Mannitol 0.135

5 pH adjusted with NaOH or HCl.

Utilizing this bath, properly cleaned steel samples of 20 cm. area were plated for minutes and 60 minutes,

Plating time 10 minutes eominutes Initial pH 4.50 5.00 5.50 4.50 5.00 5.50 Wt.galn 0.0095 0.01 0.016 0.0274 0.0345 0.0434 PlatingratmRXlO... 0.48 0.50 0.80

Turbidity none none none none none none the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the followingresults:

Plating time 10 minutes 60 minutes rmuai mn. 4. 5 5.0 5. s 4. 5 5.0 a. s Wt. gain 0.0088 0. 0088 0. 015 0. 0304 0.0350 0. 0441 Plating rate, R 10 0. 44 0. 44 0.75

Turbidity none none none none none none In view of the foregoing, it will be understood that the plating bath containing mannitol alone, in amounts .Plating time. 10 minutes 60 minutes :Initiai pH 4. 50 5. 0 0. 1215 0. 159a In another series of these plating tests, an aqueous bath having the particular composition indicated below was employed:

Bath composition:

Bath No. 30-

' Nickel chloride m.p.l 0.0675 Sodium hypophosphite m.p.l 0.225 Pyruvic acid .'.m.p.l 0.135

.Sodium succinate m.p.l 0.06 Stabilizing ion: Pb++ p.p.m 1.0

pH adjusted with NaOH and HCl.

Utilizing this plating bath, properly cleaned steel samples of '20 cm. area were plated for 10 minutes and 60 minutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the following results:

Plating time 10 minutes 00 minutes Initial H....... 4. 4s 4. 91 Wt. ain 0.1572 0.1080

In these plating tests, it will be observed that the 10 minute rates are relatively low, however, the weight of plating deposited in one hour is quite high. This indicated a long initiation period for the plating reaction.

In another series of these plating tests, an aqueous bath having the particular composition indicated below was employed:

Bath composition:

Bath No. 31-

Nickel chloride m.p.l 0.0675 Sodium hypophosphite m.p.l 0.225 Levulinic acid m.p.l 0.2025 7 Sodium succinate m.p.l 0.06 Stabilizing ion: Pb++ .p.pm.. 1.0

pH adjusted with NaOH.

It is noted that the amount of levulinic acid is more than that needed to complex all of the nickel ions in the plating bath (about 50% excess).

Utilizing this bath, properly cleaned steel samples of 20 cm. area were plated for 10 minutes and 60 minutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the following results:

Plating time 10 minutes 60 minutes Initial pH 4. 00 4. 52 5. 02 4.00 4. 52 5.02 Wt. gain 0. 0667 0. 0968 0.0872 0.1422 0.1870 0. 2055 Plating rate, RXIOL 3. 34 4. 84 4. 36

Turbidity none none none none none none Bath composition:

Bath No. 32

Nickel chloride m.p.l..- 0.0675 Sodium hypophosphite m.p.l 0.225 Trimethylamine m.p.l 0.135 Stabilizing ion: Pb'H ..p.p.m 1.0

pH adjusted with HCl.

To the Bath No. 32 increasing amounts of sodium succinate were added from to 0.09 m.p.l. and corresponding plating tests were performed on properly cleaned steel samples of 20 cm. areas for 10 minutes and 60 minutes, the volume of the bath being 50 cc. and the temperature thereof about 99 C., with the follow- Suc0inate=,'m.p.l.'. 0.06

Plating time (min) 10 5. 53 6. 0 0. 090B 0. 0715 4. 34 3. 57 none none Succinate, m.p.l 0.06 0.09

Plating time (min.) -L'; 60 10 60 5. 03 5. 03 0. 0952 O. 2028 4. 76 none none In view of the foregoing, it will be observed that the ing results: optimum pH for the Bath No. 33 appears to be around Suecinate, m.p.l none 0.03

Plating time (min) 10 V 50 1o 00 Initial nT-r 4.66 4. 00 4.52 4.52 Weight gain 0. 0044 0. 0344 0. 0588 0. 1052 Plating rate, R 10 0. 22 2. 94 Turbidity none none none none Buccinate, ni.p.1-.-- 500 i p .00

Plating time (min) 10 H 60 10 60 Initial pH I 3.03 4.5 5.04 3.03 4.5 V 5.04 4.55 4.55 weight gain 0. 0010 0. 0841 0. 0920 0.1104 0.1514 0.1034 0. 0988 0.2102 Platin rate, RXIOL 3.05 4.20 4. 0e 7 4.04 Turbidity none none none none none none none none In view of the foregoing, it will be observed that the 5.0 and that the addition of succinate over about 0.06 chelating of the nickel ions in the Bath No. 32 gives exm.p.l does not appear to give an equivalent improvement. ceedingly low plating rates, which are boosted by the ad- In another of these plating tests, an aqueous bath havdition of the proper amount of the exaltant at the proper ing the particular composition indicated below was em- PH ployed:

In another series of these plating tests, an aqueous I Bath composition: bath having the particular composition indicat'ed below Bath i was employed: r i Nickel chloride n'1.pl 0.0675 1 Sodium hypophosphite m.p.l 0.225 Bath composition Sodium succinate m.p.l 0.06

,Bath No. 33-

Propylenediamine m'.p.l 0.0675 Nickel chloride m: .1 0.0675 stablhgms 3 b. --'----,--'p-p-m-- 7 Sodium hypophosphite -m.p.-1 0.225 P adlusted Wlth P e yl p a Utilizing this plating bath, properly cleaned steel stablllzlng 111: Pb++ -P-P' samples of 80 cm. area were plated, the bath was empH adjusted with 'HCl.

To the Bath No. 33 increasing'amounts of sodium succinnte were added from 0 to 0.09 m.p.l. and corresponding plating tests were performed on properly cleaned steel samples of 20 cm. area for 10 minutes and minutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the following results:

Bath composition:

Bath No. 35-

Nickel chloride m.p.l 0.0675' Sodium hypophosphite m.p.l 0.225 1-2 aminoethanol m.p.l 0.135 Stabilizing ion: Pb++ ...'..p.p.-m 1.0

pH adjusted with HCl.

To the Bath No. 35 increasing amounts of sodium succinate were added fromv to 0.09 m.p.l. and corresponding plating tests were performed on properly cleaned steel samples of 20 cm. area for 10 minutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the following results:

Sodium SuceinatempJ. None 0.03

Initial pH. 3. 50 4. 00 4. 50 4.05 4. 46 Wt. gain 0.0078 0.0108 0.01 0 0140 0.0326 0.0435 Platingrate, R 10 0.30 0. 54 0. 50 0.70 1.63 2. 18 urbidlt none none none none none none Sodium succinate, m.p.l 0 06 Initial pH-.. 3. 48 4. 05 4. 52 4. 95 Wt. gain 0.0128 0.0408 0.0562 0. 1067 Plating rate, RX 0. 64 2. 04 2. 81 5. 34 Turbidity none none none none Sodium Succinate m.p.l i 0. 09

Initial pH 3. 53 4. 03 4. 45 5. 02 Wt. gain 0.0247 0. 0523 0. 0760 0. 0881 Plating rate, RXIO l. 24 2. 62 3. 80 4. 46 Turbidity none none none none Substantially identical plating tests were performed using the Bath No. 35 during 60 minutes with the following results:

Sodium succinate, m.p.l- 0. 06 0. 09

Initial H..- 4. 95 3. 53 4.03 4. 45 5.02 Wt. ga n 0.0247 0. 0523 0.0760 0. 2184 In the Bath No. 35, it was observed that the pH appears to be rather critical in that the plating rates of 2.81 10- and 534x10 gmJcmF/min. correspond to the pH values of 4.52 and 4.95 at a level of 0.06 m.p.l. of succinate. V

In another series of these plating tests, an aqueous bath having the particular composition indicated below was employed:

Bath composition:

Bath No. 36-

Nickel chloride m.p.i 0.0675 Sodium hypophosphite m.p.l 0.225 Sodium succinate rn.p.l 0.06 Morpholine ..m.p.l 0.135 Stabilizing ion: Pb++ p.p.m 1.0 pH adjusted with HCl.

Utilizing this plating bath, properly cleaned steel samples'of 20 cm. area were plated for. 10' minutes and 60 minutes, the volume "of the bath being 50 cc. and the temperature thereof being about 99 C., with the following results:

In another series of these plating tests, an aqueous bath having the particular composition indicated below was employed:

Bath composition:

Bath No. 37- I Nickel chloride m.p.l-- 0.0675

' 'Sodium hypophosphite m.p.l 0.225 Semi-carbazide m.p.l 0.0675

Stabilizing ion: Pb++ p.p.m 1.0

pH adjusted with CHl.

To the Bath No. 37 increasing amounts of sodium succinate were added from 0 to 0.09 m.p.l. and corresponding plating tests were performed on properly cleaned steel samples of 20 cm. area were plated for lO minutes and 60 minutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the following results:

succinate, m.p.l none 0.03

Plating time (min.) 10 60 10 60 Initial pH 5.04 5.04 5. 00 5. 00 Wt. gain. 0.0035 0.0166 0. 0035 0. 0900 Plating rate, 11x10 0.18 3.18 Turbidity none none none none Succinate, m.p.i 0.06

Plating time (min.) 10 00 10 60 Initial pH 4.53 4.53 5.00 5. 00 Wt. gain 4 0. 0024 0.1150 0. 0722 0.1390 Plating rate, RX 1 3.12 3. 61 Turbidity none none none none succinate, m.p.l 0.09

Plating time (min.) 10 00 10 00 Initial pH.... 5. 50 5.50 5. 03 5. 03 Wt. gain 0.0720 0.1540 0. 074 0.1011 Plating rate, RX104 3. 60 3. 70 Turbidity none none none none It is noted that in the Bath No. 37 with 0.06 m.p.l. of succinate and at a pH of 5.5, the 10 minute rate is substantially equal to that obtained at a pH of 5.0, but that in the 60 minute plating tests the weight gain of the plating is substantially higher at the higher pH.

In another series of these plating tests, an aqueous bath having the particular composition indicated below was employed:

Bath co mposition: Bath No. 38-'- Nickel chloride ....m.p.l.. 0.0675 Sodium hypophosphite ..m.p.l.. 0.225 Sodium succinate m.p.l 0.06 Aminoacetic acid (glycine) m.p.l. 0.135 Stabilizing ion: Pb p.p.m 1.0

pH adjusted with HCl andNaOI-I.

Utilizing this plating bath, properly cleaned steel samples of 20 cm. area were plated for 10 minutes and 60 minutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the follow- In another series of these plating tests',--aii aqueous bath having the particular composition indicated below ycle 6 7 8 9 was employed: U 1 2-0 2-20 2-2 2-2 20 at composition: 5 ma P Wt. gain, gms 3. 94 1.95 2.38 2.37 2.31 Bath No. 39- glltuehminflt 102 65 78 7: 74 I 0 i1. ow ra e, co. m 50 .5 55 a 5 55 Nuke] chlonde "7 0-0675 Platlngrate, RX10 4.83 5.00 5.42 5.32 5.28 Sod1um hypophosphlte m.p.l 0.225 Sodium succinate m.p.l 0.06 Beta-alanine m.p.l 0.135 10 73 11 12 13 Stabilizing ion: Pb++ p.p.m 1.0 pH adjusted w N H and 5531 3625 it? 2:53 2:38 a 2:38 V I r v i H W t.gain ,g 2.50 2.86 3.61 8.08 Utilizing this plating bath, properly cleaned steel 5 313 555 Gav-din g 28 2 samples of cm. area were plated for 10'rninutes and 15 Plating rate, Pl 10 .III 5. '58 6.10 6.00 6.28 60 mlnutes, the volume of the bath being 50 cc. and the temperature thereof being about 99 C., with the fol- 14 15 16 17 18 lowing results: I.

' 6.70 6.50 5.51 6.40 6.28- z 6. 50 5.80 6. 27 6.11 5. 07 mitialpH nu -uu 4.50 5.05 5.52 g; 1 8011 new niteff mm 40 52 52 50 48 Plating't'lme (mi1'1.) 10 60 10 60 10 0 Plating rate,RX10 2.45 4.75 5.43 5.72 5.93

Wt.galn. 0.0772 0.1508 0.00 0.1854 0.00 0.1001 Excess of Stabilizing 1011s D Platingratc,RX10 3.86 4.76 4.83

mmarpH; 603 M5 yc e N0 1 v .27 5.00 5.00 6.48 6.50" Plating time (min) 10 60 10 2.01 5.80 5.80 6.20 6.18 4.04 WL galn 0.0042 0.1085 0.0022 '42 40 40 44 Pl t ,R 0* 4-7 4.61 6.55 6.03 7.55 8.33 7.88

In another of these plating tests, an aqueous bath having the particular composition indicated below was employed:

Bath composition:

Utilizing this plating bath properly cleaned steel 0551-. ples of 80 cm. area were plated. The bath was employed in a continuous plating system having a plating chamber volume of 300 cc., the volume of thejbath being 1 liter and the temperature-thereof being about 100 C. In this plating test, the plating bath was regenerated after each cycle by the addition of nickel chloride, sodium hypo- 'phosphite and sodium hydroxide in the reservoir, in themanner disclosed in the Talmey and Crehan patent, and the'fdllowing results were obtained:

After the sixth and twelfth cycles 0.009 m.p.l. of amino-- acetic acid were added (10%).

Also it is noted that the plating rate of the Bath No. 40 is dependent 'upon the phosphite concentration, whereby the plating rate actually improves as the continuous operat'ion proceeds without resulting in nickel phosphite' precipitation. v

In another of these plating tests, an aqueous bath having the particular composition indicated below was. employed:

Utilizing this plating bath properly cleaned steel samples of 80 cm. area were plated. The bath was M employed in a continuous plating system having a plating W Q 1 2 3 4 chamber volume of 300. cc., the volume of the bath being" I V I 0 1 liter and the temperature thereof being about 100 C.v Initial P -8 In this"plating test, the plating bath was regenerated after 1 0101 111..-. 6.08 5.08 6.26 0.21 wt gaj n,gms 165 m0 each cycle by the addition of nickel chloride, sodium Time min 04 114 02 100 Sow-how we, w/mm" 61 62 56 hypophosph te and sodium hydroxlde 1n the VIESCIVOII', 1n Plating rate, R 10 5.06 5.10 5.00 4. the manner dISQIOSed 1n the .Talmey and Crehan patent,

-' i 1 65 and the following results were obtained:

Cycle No h 1 2 8V 4 5 0 7 Initial H 6.50 6.45 6.68 6.51 6. 45 6.22 5.08 Finalp 5.60 5.80 5.00 5. 00 5.60 5.00 5.82 Wt. gain, gms..- 4.76 :5.86 5.41 6.28 7.64 6.14 4.50 Time, min 120 96 100 123 100 $0111. flow rate, 00. 47 57 59 57 46 52 57 Plating rate, RX104 4. 07 6.70 7.02 7.84 7.75 6. 96 5. 63 Turnover, m.p.l 0.0127. 0.0270 0.0414 0 0500' 0.0808 0.0072

Addition of 2.0 p.p.m. Pb and 1.0 ppm. To.

31 For the purpose of establishing a standard of comparison, a simple aqueous citric acid plating bath of the present type was prepared that had the following composition: Bath composition:

Bath No. 42- M.p.l. Nickel chloride 0.0675 Sodium hypophosphite 0.225 Citric acid 0.0675

In a number of portions of Bath No. 42 at different pH, adjusted with NaOH and HCl, each having a volume of 32 Bath composition:

Bath No. 43 M.p.l. Nickel chloride 0.0675 Sodium hypophosphite 0.225 Malic acid 0.135

In a number of portions of Bath No. 43 at difierent pH, adjusted with NaOH and HCl, each having a volume of 50 cc. and a temperature of about 100 C., properly cleaned steel samples, each of a total raea of cm were plated in 10 minute rate tests with the following results:

50 cc. and at a temperature of about 100 C., properly cleaned steel samples, each of a total area of 20 cm, were plated in 10 minute rate tests with the following results:

The simple aqueous malic acid Bath No. 43 was modified by adding thereto different exaltants, each in the amount of 0.0675 m.p.l., and similar 10 minute plating Initial pH 4.98..." 5.49"... Wt. gain (g.).-. 0.0260.-- 0.0311.-- Platingrate.RXl0 1.30..." 1.56...

Plating time (Min.). Final pH Bath appear. (hot) Bath appear. (cold) Black precipt. none none. Plating appear smoot smooth, smooth, smooth, bright; bright. bright. bright.

bright.

The simple aqueous citric acid Bath No.,42 was modified by adding thereto different exaltants, each in the amount of 0.0675 m.p.l. and similar 10 minute plating rate tests were conducted on identical properly. cleaned steel samples with the following results:

. Alpha Exaltant Glycine Alpha amino- Aspartic alanine buytric acid acid Wt. gain (g.)..-- Plating rate, RXlO .31. Plating time (min.) 10. 10 10. Initial pH 6. 48-.. 7. 07. 5. 42 6.82. Final pH 5. 42.-. 5. 95..-" 4.47-.- 5.72. Bath appear. (hot) clear, clear, clear, clear,

blue. blue green blue Bath appear. (cold) do.. do. do Do. Black precipt none none none-. none. Plating appear smooth, smooth, smooth, smooth bright. bright. bright. bright Exaltant Malonic Succinic Glutaric Adipio acid acid acid acid Wt. gain (g 0.0614" 0.0605. Plating rate, RXiO 3.07--. 3.03.. Plating time (mm 10.... 10. Initial pH 5.49.- 4.92. Final pH 5.00..- 4.84. Bath appear. (cold) clear, clear,

green green. Bath appear. (hot) ...do Do. Black precipt none none.-. none. Plating appear smooth, smooth, smooth,

bright. bright. bright.

For the purpose of establishing a standard of comparison a simple aqueous malic acid plating bath of the present type was prepared that had the following'coniposition:

' rate tests were conducted on identical properly cleaned steel samples with the following results:

. Alpha- Exaltant Glycine Aiphaamino Aspartic alanine butyrlc acid acid Wt. gain 0.0846--. 0.0729... 0.0640--. 0.0641. Platingrate,RXi0 4.23"--- 3.65."--. 3.23"-.- 3.31. Plating time (min) 10 10 10 10. Initial H 6.42.-- 6.08".-- 5.42.-." 6.96. Finalp 4.92-....- 4.78.-- 4.58..." 5.43. Bath appear. (hot) clear, clear, clear, clear,

blue. blue green. blue Bath appear. (cold) -..do..-. --.do. 0.... Do. Black precipt nonenone none none. Plating appear smooth, smooth, smooth, smooth,

bright. bright. bright. bright.

Exaltant Malonic Succlnic Glntaric Adiplc acid acid acid acid Wt. gain (g.) 0.0732--. 0.0723--- 0.0638.-. 0.0615 Platingrate, RX10 3.66. 3.62-.-" 3.28--- 3.08. Plating time (min.) 1 1 10 10. Initial H 5.52 5.05- 5.62-.-" 4.86. Finalp 4.88--- .63 3.08. Bath appear. (hot) clear, clear. clear, clear,

green green green. green Bath appear. (cold) do do do Do. Black Precipt none none. none.. none. Plating appear smooth, smooth, smooth, smooth, bright. right bright. bright.

For the purpose of demonstrating the exalting eifects of a number of simple short chain saturated aliphatic monocarboxylic acids, further plating tests were conducted involving a number of plating baths of the nickel cation-hypophosphite anion type containing various ones of the ehelating agents previously described; and in these tests inpach instance a volume of 50 cc. of the bath sition:

Bath No. 44: M.p.l. Nickel sulfate 0.08 Sodium hypophosphite 0.23 Hydroxyacetic acid 0.20

In these plating tests, Bath No. 44 was used containing no propionic acid (as a standard) and different quantitles of propionic acid as indicated below and with the following results:

Propionic acid (m.p.l.). none 0.03 0. 06 initial pH 4. 6 0. 0752 In a second series of these plating tests, an aqueous plating bath was employed that had the following composition:

Bath No. 45: M.p.l. Nickel sulfate 0.08 Sodium hypophosphite 0.23 Malic acid 0.16

In these plating tests, Bath No.45 was used containing no propionic acid ('as a standard) and different quantitles of propionic acid as indicated below and with the following results:

Propionic acid (rn.p.l.) 0.06 Initial pH; 4. 60 Weight gain (g.) 0 0664 Plating rate, RXlO 4 3.32 Final pH 4. 5

In a third seriesof these plating tests, an aqueous plating bath was employed that had the following composition:

Bath No.46: M.p.l. Nickel sulfate 0.08 Sodium hypophosphite 0.23 Lactic acid 0.20

In these plating tests, Bath No. 46 was used containing no propionic acid (as a standard) and different quantities of propionic acid as indicated below and with the following results: Y

Propionie acid (m.p.1.) none 0. 03 0. 06 Initial pH 4. 63' 4. 60 4. 60 Weight gain (g.) 0 0684 0 0783 0.0843 Plating rate, RX 3. 42 8. 91 4. 21 Final pH 4. 0 3. 9 4. 0

In a fourth series of these plating tests, an aqueous plating bath was employed that had the following composition:

Bath No. 47: M.p.l. Nickel sulfate 0.08 Sodium hypophosphite 0.23 Aminoacetic acid I 0.16

Propionlc acid (in 1) Initial pH H e? retrace $0000? In a fifth series of these plating tests, an aqueous plating bath was employed that had the following composition:

Bath No. 48: M.p.l. Nickel sulfate n 0.08 Sodium hypophosphite 0.23 Propylenerliamine 0.16

In these plating tests, 'Bath No. 48 was used containing no propionic acid (as a standard) and diiferent quantities of propionic acid as indicated below and with the following results:

Proplonic acid (m.p 1) none 0. 03 0.06 Initial pH 4.64 4. 4. 64 Weight gain (g 0 0175 0.0300 0.0370 Plating rate, RXIOL.-- 0. 88 1. 50 1.85

in pH 3.4 4 1 4.2

In additional series of these plating tests, Bath No. 46 was again employed containing different amounts of hutyric acid and valeric acid as indicated below and with the following results:

Butyric acid (m.p.l.)....-. 0. 03 0. 06 Valerie acid (m.p.l.) 0. 03 0. 06 Initial pH 4. 64 4. 62 4. 64 4. 60 WelZhi', gain (g.) 0. 0740 0. 0803 0. 0749 0. 0856 Plating rate, RXlO 3. 4. 0i 3. 4. 28 Final pH 4. 0 4. 0 4. 0 4. 0

In a further series of these plating tests, Bath No. 47 was again employed containing different amounts of butyric acid and valenic acid as indicated below and with the following results:

Butyric acid (1n.p.l 0. 03 0.06 Valerie acid (n.1.p.l 0.03 0.06 Initial pH 6.24 6.22 6.20 6. 20 Weight gain (g.) 0.0921 0.0996 0.0902 0 0896 Plating rate, RXlOL. 4. 61 4.98 4. 51 4. 48 Final pH 5. 4 5. 5 5. 4 5. 4

where R=plating rate c,,=concentration of organic acid m=slope R =intercept constant or unexalted plating rate.

Differentiation of (1) yields the equation:

(2) Eric The value of m is a definite functional property of the organic acid used as an exalting additive, and the numerical value thereof indicates the degree of exaltation of the normal or unexalted plating rate of the particular plating bath by the particular organic acid.

Recapitulating, in the continuous plat-ing system, the malic acid-lactic acid-Su ccinate bath, the malic acidglycine bath and the malic acid-succinate bath are generally preferred both from the standpoint of economy and performance. Specifically, the malic acid-lactic acidsuccinate plating bath, although somewhat slower than the other two last-mentioned plating baths with regard to plating rate, is productive of a nickel plating upon steel that exhibits excellent adhesion (even on steel castings) as. it may be employed at a pH as low as 4.0 to

5.0, and since this plating both has a long useful life, as it will retain nickel phosphite in solution even at concentrations up to 1 molar. Specifically, the malic acidglycine plating bath exhibits an exceedingly high plating rate and retains the nickel phosphite in solution over the exceedingly wide pH range 4.3 to 9.5 even in a concentration as high as 1 molar. Specifically, the malic acid-succinate bath has an entirely satisfactory plating rate and an optimum pH substantially at neutrality and satisfactorily holds the nickel phosphite in solution even at a concentration as high as 1 molar.

A typical malic acid-lactic acid-succinate plating bath comprises: an absolute concentration of hypophosphite ions in the range 0.15 to 1.20 moles/liter; a ratio between nickel ions and hypophosphite ions in the range 0.25 to 1.60; an absolute concentration of malic acid ions in the range 0.04 to 0.20 mole/liter;'a'n absolute concentration of lactic acid ions in the range 0.04 to 0.20 mole/liter; the total quantity of the malic acid ions and the lactic acid ions are sufficient to complex at least 100% of the nickel ions; an absolute concentration of succinic acid ions of at least 0.04 mole/liter; and a pH within the range 4.0t'o 7.0. i

'A typical malic acid-glycine'plating bath comprises: an absolute concentration of hypophosphite ions in the range 0.15 to 1.20 mole/ liter; a ratio between nickel ions and the hypophosphite ions in the range 0.25 to 1.60; an absolute concentration of malic acid ions suflicient to complex at least 100% of the nickel ions; an absolute concentration of glycine ions of at least 0.04 mole/liter;

and a pH within the range 4.3 to 9.5.

A typical malic acid-succinate plating bath comprises: an absolute concentration of hypophosphite ions .in the range 0.15 to 1.20 mole/liter; a ratio between nickel ions and hypophosphite ions in the range 0.25 to 1.60; an absolute concentration of malic acid ions sufficient to complex at least 100% of the nickel ions; an absolute concentration of succinic acid ions of at least 0.04 mole/ liter; and a pH within the range 4.0 to 7.0.

In view of the foregoing, it is apparent that there has been provided an improved process of chemical nickel plating, as well as improved plating baths therefor, wherein the baths are of the nickel cation-hypophosphite anion type, also containing a chelating agent of the character specified and substantially completely chelatihg all of the nickel ions in the bath, and also containing an exalting additive of the character specified and exalting the plating rate of the bath; The chelating agent is selected from the group having the general formula:

where: R is an aliphatic radical, X is a functional group containing a dissociable hydrogen atom and selected from the class consisting of:

o u -C-OH, NHz, =NH and-OH and Y is a functional group, containing a negative atom acting as a center of coordination and selected from the class consisting of:

OH, =0, --NH =NI-I and EN and wherein the functional groups X and Y are in alpha or beta positions to each other. The exalting additive is selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids including 3 to 5 carbon atoms and salts thereof, simple short chain saturated aliphatic dicarboxylic acids including 3 to 6 carbon atoms and salts thereof, and short chain aliphatic aminocarboxylic acids and salts thereof. The plating baths are particularly well-adapted for use in a continuous plating system as they exhibit a fast plating rate, have an exceedingly long life, and maintain nickel phosphite in solution in concentrations as high as one molar.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. The process of chemically plating with nickel a body comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of a nickel salt and a hypophosphite and a first chelating agent selected from the group consisting of malic acid and salts thereof and a second chelating agent selected from the group consisting of lactic acid and salts thereof and an exalting additive selected from'the groupconsisting of succinicacid and salts thereof, the ratio between nickel ions and hypophosphite ions, in said bath being in the range 0.25 to 1.60, the absolute concentration of hypophosphite ions in said bath being in the range 0.15

to 1.20 mole/liter, the absolute concentration of malic acid ions in said bath being in the range 0.04 to 0.20 mole/liter, the absolute concentration of lactic acid ions being at least 0.04 mole/liter soas substantially to exalt the plating rate of said bath.

2. The process of chemically plating with nickel a body comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a hot bath comprising a aqueous solution of a nickel salt and a hypophosphite and a first chelating agent selected from the group consisting of malic acid and salts thereof and a second chelating agent selected from the group consisting of lactic acid and salts thereof and an exalting additive selected from the group consisting of succinic acid and salts thereof, the temperature of said bath being above C. and the pH of said bath being in the range 4.0 to 7.0, the ratio between nickel ions and hypophosphite ions in said bath being in the range 0.25 to 1.60 the absolute concentration of hypo- .phosphite ions in said bath being in the range 0.15 to 1.20 moles/liter, the absolute concentrationof malic acid ions in said bath being in the range 0.04 to 0.20 mole/liter, the absolute concentration of lactic acid ions in said bath being in the range 0.04 to 0.20 mole/liter,

the total quantity of said first and second chelating agents in'said bath being sufiicient to chelate at least of the nickel ions therein so as to impart to said bath a phosphite tolerance of at least about 1 mol/liter, and the absolute concentration of succinic acid ions in said bath being at least 0.04 mol/liter so as substantially to exalt the plating rate of said bath.

3. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum,

copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of nickel ions, hypophosphite ions, a chelating agent, and a separate and .different chemical type exalting additive; said agent being present in an amount sufiicient to chelate at. least 100% of the nickel 10115 in said bath so as to impart thereto a phosphite tolerance of at least about 1 mole/liter and having the general formula:

where: R is an aliphatic radical, X is a functional group containing a dissociable, hydrogen atom andv selected from the class consisting of:

and Y is a functional group containing a negative atom acting as a center of coordination and selected from the class consisting of:

OI-I, =0, -NH =NH and EN and wherein the functional groups X and Y are in alpha or beta positions to each other; said additive being present in an amount sufficient substantially to exalt the plating rate of said bath and being selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids including 3 to 5 carbon atoms and salts thereof, simple short chain saturated aliphatic dicarboxylic acids including 3 to 6 carbon atoms and salts thereof, and short chain aliphatic arninocarboxylic acids and salts thereof; wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphi te ions in said bath expressed in molar concentrations is within the range 0.25 to 1.60 and the initial pH of said bath is within the approximate range 4.0 to 11.0.

4. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of a nickel salt, an alkaline hypophosphite, a chelating agent, and a separate and different chemical type exalting additive; said agent being present in an amountsufiicient to chelate at least 100% of the nickel ions in said bath so as to impart thereto a phosphite tolerance of at least about 1 mole/liter and having the general formula:

where: R is an aliphatic radical, X is a functional group containing a dissociable hydrogen atom and selected from the class consisting of:

i -0H, NH2, =NH and OH and Y is a functional group containing a negative atom acting as a center of coordination and selected from the class consisting of:

--OH, :0, -NH2, =NH and EN and wherein the functional groups X and Y are in alpha or beta positions to each other; said additive being present in an amount suliicient substantially to exalt the plating rate of said bath and being selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids including 3 to carbon atoms and salts thereof, simple short chain saturated aliphatic dic-arboxylic acids including 3 to 6 carbon atoms and salts thereof, and short chain aliphatic aminocarboxylic acids and salts thereof; wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range of 0.25 to 1.60, and the initial pH of said bath is within the approximate range 4.0 to 11.0. l

5. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copaqueous solution of nickel ions, hypophosphite ions, a

chelating agent, and a separate andditferent chemical type exalting additive; said agent being present in an amount suln'cient to chelate. at least of the, nickel ions in said bath so as to impart thereto a phosphite toleranceof at least about 1 mole/liter and having the general formula:

and Y is a functional group containing a negative atom acting as a center of coordination and selected from the class consisting of:

-OH, =0, NH =NH and EN and wherein the functional groups X and Y are in alpha or beta positions to each other; said additive being present in an amount sufficient substantially to exalt the plating rate of said bath and being selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids including 3 to 5 carbon atoms and salts thereof, simple short chain saturated aliphatic dicarboxylic acids including 3 to 6 carbon atoms and salts thereof, and short chain aliphatic arninocarboxylic acids and salts thereof; wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 1.60, and the initial pH of said bath is within the approximate range 4.0 to 11.0

6. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of nickel ions, hypophosphite ions, a chelating agent, and a separate and diiferent chemical type exalting additive; said agent being present in an amount suificient to chelate at least 100% of the nickel ions in said bath so as to impart thereto a phosphite tolerance of at least about 1 mole/liter and being selected from the group consisting of saturated aliphatic hydroxycarboxylic acids and salts thereof; said additive being present in an amount sufiicient' substantially to exalt the plating rate of said bath and being selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids including 3 to 5 carbon atoms and salts thereof, simple short chain saturated aliphatic dicarboxylic acids including 3 to 6 carbon atoms and salts thereof, and short chain aliphatic aminocarboxylic acids and salts thereof; wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is Within the range 0.25 to 1.60, and the initial pH of said bath is within the approximate range 4.0 to 7.0. v

7. The process of chemically plating with nickel a body essentially comprising an element selected from the groupconsisting of iron, cobalt, nickel, aluminum, copper, silver,gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of nickel ions, hypophosphite ions, a chelating agent, and a separate and different chemical type exalting additive; said agent being present in an amount sufficient to chelate at least 100% of the nickel ions in said bath so as to impart thereto a phosphite tolerance of at least about 1 mole/liter and being selected from the group consisting of saturated aliphatic hydroxycarboxylic acids and salts thereof; said additive being present in an amount sufficient substantially to exalt the 39 plating rate of said bath and being selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids including 3 toScarbon'atomsand salts thereof; wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar 'concentrations'is within the range. 0.25 to 1.60, and the initial pH of said bath is within the approximate range 4.0 to 7.0. .11 i 1 8. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and,platinum, which corn,- prises .contacting said body with a bath comprising an aqueou's'solution of nickel ions, hypophosphite ions, a chelating agent, and a separate anddifierent chemical type exalting'additive; said agent being present in an amount sufficient to chelate at least 100%. of the nickel ions in said bath so as to impart thereto a phosphite tolerance of at least about 1 mole/liter and being selected from the group consisting of saturated aliphatic hydroxycarboxylic acids and salts thereof; said additive being present in an amount sufficient substantially toexalt the plating rate of said bath and being selectedqfrom the group consisting of simple short chain saturated aliphatic dicarboxylic acids including 3 to 6 carbon atoms and salts thereof; wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 1.60, and the initial pH of said bath is within the approximate range 4.0 to 7.0.

9.. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of nickel ions, hypophosphite ions, a chelating agent, and a separate and different chemical type exalting additive; said agent being present in an amount sufficient to chelate at least 100% of the nickel ions in said bath so as to impart thereto a phosphite tolerance of at least about 1 mole/liter and being selected from the group consisting of lactic acid and salts thereof; said additive being present in an amount sufiicient substantially to exalt the plating rate of said bath and being selected from the group consisting of succinic acid and salts thereof; wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is' within the range 0.25 to 1.60, and the initial pH of said bath is within the approximate range 4.0 to 7 .0.

10. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of nickel, ions, hypophosphite ions, at chelating agent, and a separate; and dilferent chemical type exalting additive; said agent being present in an amount sufficient to chelate at least 100% of the nickel ions in said bath so as to impart thereto a phosphite tolerance of at least about 1 mole/liter and being selected from the group consisting of malic acid and salts thereof; said additive being present in an amount sufiicient substantially to exalt the plating rate of said bath and being selected from the group consisting of succinic acid and salts thereof; wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratiolbetween nickel ions and hypophosphite ions in saidbath expressed in molarconcentrations is within the 40 range 0.25 to 1.60, and the initial pH of said bath is within the approximate range 4.0 to 7.0.

11. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of a nickel salt and a hypophosphite and a chelating agent selected from the group consisting of malic acid and salts thereof and an exalting additive selected from the group consisting of succinic acid and salts thereof, the ratio between nickel ions and hypophosphite ions in said bath being in the range 0.25 to 1.60, the absolute concentration of hypophosphite ions in said bath being in the range 0.15 to 1.20 mole-liter, the abso lute concentration of malic acid ions in said bath being suificient to chelate at least 100% of the nickel ions therein so as to impart to said bath a phosphite tolerance of at least about 1 mole/liter, and the absolute concentration of succinic acid ions in said bath being at least 0.04 mole/liter so as substantially to exalt the plating rate of said bath.

12. The process of chemically plating with nickel a body comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a hot bath comprising an aqueous solution of a nickel salt and a hypophosphite and a chelating agent selected from the group consisting of malic acid and salts thereof and an exalting additive selected from the group consisting of succinic acid and salts thereof, the temperature of said bath being above C. and the pH of said bath being in the range 4.0 to 7.0, the ratio between nickel ions and hypophosphite ions in said bath being in the range 0.25 to 1.60, the absolute concentration of hypophosphite ions in said bath being in the range 0.15 to 1.20 mole/liter, the absolute concentration of malic acid ions in said bath being sufficient to chelate at least of the nickel ions therein so as to impart to said bath a phosphite tolerance of at least about 1 mole/ liter, and the absolute concentration of succinic acid ions in said bath being at least 0.04 mole/liter so as substantially to exalt the plating rate of said bath.

13. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of nickel ions, hypophosphite ions, a chelating agent, and a separate and different chemical type exalting additive; said agent being present in an amount sufficient to chelate at least 100% of the nickel ions in said bath so as to impart thereto a phosphite tolerance of at least about 1 mole/liter and being selected from the group consisting of saturated aliphatic hydroxycarboxylic acids and salts thereof; said additive being present in an amount sutficient substantially to exalt the plating rate of said bath and being selected from the group consisting of short chain aliphatic aminocarboxylic acids and salts thereof; wherein the absolute concentration of hypophosphite ions in said bath expressed in mole/liter is within the range 0.15 to 1.20, the ratio between nickel ions and hypophosphite ions in said bath expressed in molar concentrations is within the range 0.25 to 1.60, and the initial pH of said bath is within the approximate range 4.3 to 9.5.

14. The process of chemically plating with nickel a body essentially comprising an element selected from the group consisting of iron, cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum, which comprises contacting said body with a bath comprising an aqueous solution of nickel ions, hypophosphite ions, a chelating agent, and a separate and different chemical type exalting additive; said agent being present in an amount sufiicient to chelate atleast 100% of the nickel ions in said bath 

1. THE PROCESS OF CHEMICALLY PLATING WITH NICKEL A BODY COMPRISING AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF IRON, COBALT, NICKEL, ALUMINUM, COPPER, SILVER, GOLD, PALLADUIM AND PLATINUM, WHICH COMPRISES CONTACTING SAID BODY WITH A BATH COMPRISING AN AQUEOUS SOLUTION OF A NICKEL SALT AND A HYPOPHOSPHITE AND A FIRST CHELATING AGENT SELECTED FROM THE GROUP CONSISTING OF MALIC ACID AND SALTS THEREOF AND A SECOND CHELATING AGENT SELECTED FROM THE GROUP CONSISTING OF LACTIC ACID AND SALTS THEREOF AND AN EXALTING ADDITIVE SELECTED FROM THE GROUP CONSISTING OF SUCCINC ACID AND SALTS THEREOF, THE RATIO BETWEEN NICKEL IONS AND HYPOPHOSPHITE IONS IN SAID BATH BEING IN THE RANGE OF 0.25 TO 1.60, THE ABSOLUTE CONCENTRATION OF HYPOPHOSPHITE IONS IN SAID BATH BEING IN THE RANGE 0.15 TO 1.20 MOLE/LITER, THE ABSOLUTE CONCENTRATION OF MALICACID IONS IN SAID BATH BEING IN THE RANGE 0.004 TO 0.20 MOLE/LITER, THE ABSOLUTE CONCENTRATION OF LACTIC ACID IONS IN SAID BATH BEING IN THE RANGE OF 0.04 TO 0.20 MOLE/LITER, THE TOTAL QUANTITY OF SAID FIRST AND SECOND CHELATING AGENTS IN SAID BATH BEING SUFFICIENT TO CHELATE AT LEAST 100% OF THE NICKEL IONS THEREIN SO AS TO IMPART TO SAID BATH A PHOSPHITE TOLERANCE OF AT LEAST ABOUT 1 MOLE-LITER, AND THE ABSOLUTE CONCENTRATION OF SUCCINIC ACID IONS IN SAID BATH BEING AT LEAST 0.04 MOLE/LITER SO AS SUBSTANTIALLY TO EXALT THE PLATING RATE OF SAID BATH. 